1. Field of the Invention
The present invention relates to a secondary battery in which a porous filling member occupies a portion of the molding space between a bare cell and a protective circuit board prior to a molding operation.
2. Description of the Related Art
In general, unlike primary batteries that are not rechargeable, secondary batteries are rechargeable batteries. Secondary batteries have come into widespread use for small electronic apparatuses, such as cellular phones, personal digital assistants (PDAs), and notebook computers. In particular, lithium secondary batteries operate at a voltage of 3.6 V and are widely used as a power source for electronic apparatuses since the operating voltage of the lithium secondary battery is approximately 3 times higher than that of nickel-cadmium (Ni—Cd) batteries or nickel-hydride (Ni-MH) batteries and the lithium secondary batteries have a high energy density per unit weight.
In general, the lithium secondary battery employs a lithium-based oxide as a positive electrode active material and a carbon material as a negative electrode active material. In addition, the lithium secondary battery can take on various shapes, such as a cylindrical shape, a square shape and a pouch shape.
The square shape secondary battery includes a square-shaped bare cell and a protective circuit module. The bare cell includes a jellyroll-type electrode assembly, a can that has an opening portion on one side and houses the electrode assembly, and a cap assembly that closes up the opening portion of the can to seal the can.
The protecting circuit module is a safety device for cutting off a circuit to break a current when the voltage of the battery is suddenly increased due to overheating or overdischarging of the battery, thereby preventing the combustion or explosion of the battery. The protective circuit module includes a protective circuit board formed by mounting various elements on a printed circuit board (PCB), and the protective circuit board is electrically connected to the bare cell through conductors, which are called lead plates.
A combination of the bare cell and the protective circuit module is called a core pack, and the secondary battery can be used in the form of the core pack. However, in general, a separate outer case is used to insulate or protect the core pack since the secondary battery is used for portable electronic apparatuses. For example, generally, the core pack is put into an outer case formed of a synthetic resin, or the bare cell and the protective circuit module of the core pack are combined to each other by molding, and labeling or tubing is performed on the combination.
However, when the bare cell and the protective circuit module of the core pack are combined to each other by molding, a molding space is increased, and it is difficult to uniformly inject a molding resin into the large molding space. Therefore, the molding resin is injected into the molding space of the core pack to a non-uniform thickness, which causes the surface of a mold that is located at the upper part of the secondary battery to be uneven, or causes the thickness of the mold of the secondary battery to be non-uniform, resulting in a large defect distribution in the battery. In addition, the molding resin injected into the molding space between the bare cell and the protective circuit module suddenly solidifies and shrinks a little. In this case, as described above, when the molding resin is injected non-uniformly, or when the molding resin is not completely injected into the molding space due to electrical connection members or elements, the amount of shrinkage of the molding resin increases. As a result, the mold of the secondary battery has a non-uniform surface, and a manufactured secondary battery has a non-uniform thickness, which results in a large defect distribution in the secondary battery.
In particular, as the functions of portable electronic apparatuses increase, high-capacity batteries are in demand, and in order to meet these demands, the width or thickness of the battery increases, which results in a large molding space for the core pack. Therefore, as described above, it is difficult to uniformly inject a molding resin into the molding space of the core pack, which causes the degree of distribution of a mold formed at an upper part of the core pack of the secondary battery to increase.
Further, since electrical connection members or elements, such as lead plates, are provided between the bare cell and the protective circuit board, the initial arrangement of the connection members or elements is upset due to the application pressure of the molding resin. Therefore, when a high application pressure of the molding resin is applied to the protective circuit board or the lead plates, the arrangement of the bare cell and the protective circuit module is upset, which results in an increase in the defective rate in secondary batteries.